Remote Imaging of Exploration Flight Test-1 (EFT-1) Entry Heating Risk Reduction

(1)

NESC-RP-12-00795

Remote Imaging of

Exploration Flight Test-1 (EFT-1)

Entry Heating Risk Reduction

David M. Schuster/NESC

Langley Research Center, Hampton, Virginia Thomas J. Horvath

Langley Research Center, Hampton, Virginia Richard J. Schwartz

(2)

Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA scientific and technical information (STI) program plays a key part in helping NASA maintain this important role.

The NASA STI program operates under the auspices of the Agency Chief Information Officer. It collects, organizes, provides for archiving, and disseminates NASA’s STI. The NASA STI program provides access to the NTRS Registered and its public interface, the NASA Technical Reports Server, thus providing one of the largest collections of aeronautical and space science STI in the world. Results are published in both non-NASA channels and by NASA in the NASA STI Report Series, which includes the following report types:

 TECHNICAL PUBLICATION. Reports of

completed research or a major significant phase of research that present the results of NASA Programs and include extensive data or theoretical analysis. Includes compilations of significant scientific and technical data and information deemed to be of continuing reference value. NASA counter-part of peer-reviewed formal professional papers but has less stringent limitations on manuscript length and extent of graphic presentations.

 TECHNICAL MEMORANDUM. Scientific

and technical findings that are preliminary or of specialized interest, e.g., quick release reports, working papers, and bibliographies that contain minimal annotation. Does not contain extensive analysis.

 CONTRACTOR REPORT. Scientific and

technical findings by NASA-sponsored contractors and grantees.

 CONFERENCE PUBLICATION.

Collected papers from scientific and technical conferences, symposia, seminars, or other meetings sponsored or

co-sponsored by NASA.

 SPECIAL PUBLICATION. Scientific,

technical, or historical information from NASA programs, projects, and missions, often concerned with subjects having substantial public interest.

 TECHNICAL TRANSLATION.

English-language translations of foreign scientific and technical material pertinent to NASA’s mission.

Specialized services also include organizing and publishing research results, distributing specialized research announcements and feeds, providing information desk and personal search support, and enabling data exchange services. For more information about the NASA STI program, see the following:

 Access the NASA STI program home page

at http://www.sti.nasa.gov

 E-mail your question to [email protected]

 Phone the NASA STI Information Desk at

757-864-9658

 Write to:

NASA STI Information Desk Mail Stop 148

NASA Langley Research Center Hampton, VA 23681-2199

(3)

National Aeronautics and Space Administration Langley Research Center Hampton, Virginia 23681-2199

NESC-RP-12-00795

Remote Imaging of

Exploration Flight Test-1 (EFT-1)

David M. Schuster/NESC

Langley Research Center, Hampton, Virginia Thomas J. Horvath

Langley Research Center, Hampton, Virginia Richard J. Schwartz

(4)

Available from:

NASA STI Program / Mail Stop 148 NASA Langley Research Center

Hampton, VA 23681-2199 Fax: 757-864-6500

Acknowledgments

The NESC team would like to recognize the Aerospace Corporation and the WB-57 High Altitude Research Program at the NASA JSC for support during this assessment. The services of these two organizations were activated deep into in the demonstration of capability (EFT-1 observation) phase of the assessment as a risk-reduction effort. While the primary aircraft was able to support the

observation, the professional attitude and dedication to preparing a second aircraft to perform the mission on such short notice was remarkable. The NESC team would also like to recognize Surface Optics for providing laboratory

measurements to quantify the surface optical properties of the MPCV TPS. The test results had a significant impact regarding the observation strategy to acquire the capsule at long range.

The use of trademarks or names of manufacturers in the report is for accurate reporting and does not constitute an official endorsement, either expressed or implied, of such products or manufacturers by the National Aeronautics and Space Administration.

(5)

Remote Imaging of Exploration Flight Test-1 (EFT-1)

(6)

Report Approval and Revision History

NOTE: This document was approved at the May 19, 2016, NRB. This document was submitted to the NESC Director on June 10, 2016, for configuration control.

Approved: Original Signature on File 6/15/16

NESC Director Date

Version Description of Revision Office of Primary

Responsibility Effective Date 1.0 Initial Release Dr. David Schuster,

NASA Technical Fellow for

Aerosciences, LaRC

(7)

Technical Assessment Report

1.0

Notification and Authorization

Mr. Gavin Mendeck, the Entry, Descent, and Landing (EDL) Phase Engineer for the Multi-Purpose Crew Vehicle (MPCV) Program (Vehicle Integration Office/Systems & Mission Integration) at Johnson Space Center (JSC), requested a risk-reduction assessment pertaining to the use of quantitative imagery to independently provide Exploration Flight Test-1 (EFT-1) heat shield surface temperatures during reentry. A NASA Engineering and Safety Center (NESC) initial evaluation was approved on June 7, 2012. Dr. David Schuster, NASA Technical Fellow for the Aerosciences, was selected to lead this assessment. The assessment plan was approved by the NESC Review Board on June 28, 2012. The assessment plan identified the EFT-1 imagery team within the NESC and defined the team’s mission, membership, responsibilities, and conduct of operations.

The key stakeholders for this assessment were Gavin Mendeck, the MPCV Program EDL Phase Engineer; Pete Huseman, MPCV Program Aerosciences Senior Manager (Lockheed Martin); Joe Olejniczak, MPCV Aerosciences Manager at Ames Research Center; and Stan Bouslog and John Kowal within the JSC Thermal Protection System (TPS) discipline area.

(12)

2.0

Signature Page

Submitted by:

Team Signature Page on File – 6/22/16

Dr. David M. Schuster Date

Significant Contributors:

Mr. Thomas J. Horvath Date Mr. Richard J. Schwartz Date

Signatories declare the findings, observations, and NESC recommendations compiled in the report are factually based from data extracted from program/project documents, contractor

(13)

reports, and open literature, and/or generated from independently conducted tests, analyses, and inspections.

(14)

3.0

Team List

Name Discipline Organization

Core Team

David M. Schuster NESC Lead LaRC

Thomas J. Horvath Deputy Lead LaRC

Adam Amar Numerical Modeling JSC

Frank Brody NOAA/SMG JSC

Melinda Cagle Project Manager (EDL) LaRC

Tim Garner Spaceflight Meteorology Group JSC/NOAA

David Gibson CFLOS JHU-APL

Wayne Hensley Landing Support Officer JSC/USA

Stephanie Hamrick MTSO Program Analyst LaRC

Jose Kalil Lead Landing Safety Officer JSC

Michael Kelly CFLOS JHU-APL

Stephen Kennerly Night Vision and Electronic Sensors JHU-APL

Robert Kerns Communications LaRC

Mark McDonald EFT-1 Lead Flight Dynamics Officer JSC/USA

Gavin Mendeck EFT-1 Interface JSC

David Mercer Sensor Calibration LaRC/Lites

Shann Rufer Asset Coordinator LaRC

Richard Schwartz Mission Modeling LaRC/AMA

Jan Shumaker P-3 Test Manager NAVAIR

Daniel Smith MPCV Program Imaging Working Group JSC/Jacobs

Thomas Spisz Image Analyst JHU-APL

Steve Tack P-3 Imaging Specialist NAVAIR

Jeff Taylor Sensor Modeling & Analysis JHU-APL

Daniel Winterhalter Technical Lead for Robotics JPL

Harry Verstynen Asset Communications LaRC

Joe Zalameda Sensor Calibration LaRC

Administrative Support

Melinda Meredith Project Coordinator LaRC/AMA

Linda Burgess Planning and Control Analyst LaRC/AMA

Dee Bullock Technical Writer LaRC/AMA

3.1

Acknowledgements

The NESC team would like to recognize the Aerospace Corporation and the WB-57 High

Altitude Research Program at the NASA JSC for support during this assessment. The services of these two organizations were activated deep into in the demonstration of capability (EFT-1 observation) phase of the assessment as a risk-reduction effort. While the primary aircraft was able to support the observation, the professional attitude and dedication to preparing a second aircraft to perform the mission on such short notice was remarkable. The NESC team would also

(15)

like to recognize Surface Optics for providing laboratory measurements to quantify the surface optical properties of the MPCV TPS. The test results had a significant impact regarding the observation strategy to acquire the capsule at long range.

(16)

4.0

Executive Summary

A Measure of Performance (MOP) identified with an Exploration Flight Test-1 (EFT-1) Multi-Purpose Crew Vehicle (MPCV) Program Flight Test Objective (FTO) (OFT1.091) specified an observation during reentry though external ground-based or airborne assets with thermal detection capabilities. The objective of this FTO was to be met with onboard Developmental Flight Instrumentation (DFI), but the MOP for external observation was intended to provide complementary quantitative data and serve as a risk reduction in the event of anomalous DFI behavior (or failure). Mr. Gavin Mendeck, the Entry, Descent, and Landing (EDL) Phase Engineer for the MPCV Program (Vehicle Integration Office/Systems & Mission Integration) requested a risk-reduction assessment from the NASA Engineering and Safety Center (NESC) to determine whether quantitative imagery could be obtained from remote aerial assets to support the external observation MOP. If so, then a viable path forward was to be determined, risks identified, and an observation pursued. If not, then the MOP for external observation was to be eliminated.

As part of this assessment:

 A review of measurement platforms and instrument capability was highlighted and aerial-based capabilities were preferred.

 Risks associated with the desired aerial observation were identified and described and mitigated during the observation.

 Available tools and techniques to characterize and reduce risk were described and exercised.

 A quantitative remote infrared-based observation from a crewed Navy NP-3D aircraft (referred to as BH-300) to provide engineering quality data was determined to be viable, and an observation campaign was successfully planned and executed. The coordination of the planning and mission operations was described.

 A request to expand the responsibilities of the NESC mission operations team to include the coordination of two additional aerial assets sponsored by the MPCV Program and NASA Public Affairs was identified along with steps taken to mitigate additional risk. The aircraft included a second Navy NP-3D aircraft (referred to as BH-340) to observe late stage

recovery events such as the parachute deployment sequence, and an unmanned aerial vehicle (UAV) used for real-time video streaming.

 Risks that matured during the observation were identified and a chronology-based description of how the NESC mission operations team made informed decisions was presented.

 An optional analysis task to infer heat shield surface temperature from the calibrated thermal imagery was pursued based upon the quality of the acquired infrared imagery.

 Global surface temperature was inferred from calibrated infrared measurements and

compared to surface temperatures reconstructed from in-depth measurements from two DFI thermocouples (TC). TC-derived temperatures were approximately 100 °F above the image-derived surface temperatures.

(17)

 Uncertainties of the image-derived surface temperature are dominated by uncertainties in the Avcoat surface emissivity and transmissivity of the atmosphere. Estimated uncertainty of the imaged derived surface temperature is ±15 °F.

 Uncertainties in the surface-derived temperatures from the TCs was not in scope of this assessment but the large difference between the two measurement techniques suggests a high-fidelity uncertainty analysis is needed of the material properties of charred and ablated Avcoat that are currently used in the TC reconstruction process.

 The appendices provide further documentation of laboratory test results used to optimize the infrared sensor configuration, mission planning, data assimilation, and procedures associated with sensor calibration and aircraft operations.

Because the observation of the capsule at peak heating was expected to occur over a remote broad area of ocean, surface-based imaging assets were dismissed. Airborne platforms with imaging capability were identified and several eliminated due to their inability to reach the desired observation location with sufficient loiter time. The optical performance of the

remaining aerial platforms to provide adequate spatial resolution was assessed. Tools developed to simulate optical performance were exercised. Risks associated with schedule availability of the aircraft to support the observation were balanced against cost, sensor requirements for long-range acquisition/tracking, and with crew operational experience. A recommendation was accepted by the MPCV Program Flight Test Management Office (FTMO) and the NESC Review Board to pursue a thermal observation using an existing imaging asset within the Department of Defense (DoD) with demonstrated capability.

To obtain the thermal imagery, the NESC team leveraged from mission planning tools developed under NESC assessment 07-048-E [ref. 1] and successfully utilized by the Space Shuttle

Program (SSP)-sponsored Hypersonic Thermodynamic Infrared Measurement (HYTHIRM) team to provide global thermal images of seven SSP flights during hypersonic descent from 2009 to 2011 [refs. 2-19], the SpaceX Dragon capsule during its inaugural reentry in 2010, and the recovery of a SpaceX Falcon 9 first stage during a flight test in 2014 [ref. 20]. The concept of operations for the EFT-1 observation base lined the use of a Navy aircraft (BH-300). An Agency aircraft (WB-57) was later identified as a viable asset for risk mitigation if conflicts with the Navy asset developed. This risk was recognized several days before the EFT-1 launch; the WB-57 was activated as a backup but not flown because the conflict with the DoD asset was resolved. The team planned for but was not required to support off-nominal capsule reentry trajectories, nor were aircraft search and recovery services required. Opportunities to obtain spectral measurements of the afterbody wake and/or thermal measurements were considered but not pursued due to limitations of the existing Navy sensors. The assessment was considered complete with acquisition of the flight thermal imagery. However, subsequent approval of the optional data analysis extended the assessment timeline.

Based upon the success of the assessment, the MPCV Program requested the Scientifically Calibrated In-Flight Imagery (SCIFLI) team submit a budget request to perform an observation of the crew capsule’s flight test Exploration Mission-1 (EM-1) that is targeted for September 2018 and planning has commenced. The DoD has entered into several collaborative efforts with

(18)

the SCIFLI team to develop a nationally managed unmanned aerial system (UAS) program to provide flexible, lower-cost, higher-quality measurement capability for civilian- and defense-related developmental/operational flight testing.

After the successful observation on December 5, 2014, the NESC team held internal reviews to identify and document lessons learned. The assessment findings, observations, and NESC recommendations presented in Section 8.0 can be summarized as:

 An external observation can provide unique non-evasive thermal protection system (TPS) performance data to complement in-situ instrumentation, which the latter often presents power, weight, and size challenges with limited spatial coverage.

 A crewed aircraft was used to successfully obtain engineering quality global surface temperature on a human-rated capsule of considerably smaller dimension than previously demonstrated.

 While capable, cost considerations of crewed platforms should be rigorously evaluated, with the flexibility in asset positioning to avoid weather constraints, endurance (time on station), and sensor limitations.

 The need for more affordable airborne imaging systems with enhanced capability is tied to future Agency and National flight test and evaluation (T&E) needs and the level of risk a development flight test program is willing to accept.

 NASA and DoD should explore and identify common interests and investments to maintain and advance flight (and in particular, hypersonic) T&E infrastructure.

(19)

5.0

Assessment Plan

The assessment plan was initiated from concerns that the MOP specifying a quantitative, spatially resolved thermal observation of the EFT-1 capsule during reentry though external ground-based or airborne assets could not be met. The objective of this assessment was to provide recommendations to the MPCV Program on the ability to provide global heat shield temperature maps derived from engineering-quality thermal imagery obtained from an electro-optical asset during EFT-1 reentry. The assessment, as proposed, consisted of three phases: (1) an assessment of measurement capability, (2) a demonstration of capability through an infrared observation, and (3) an optional data analysis phase if imagery was successfully

obtained. During the first phase, the NESC team reviewed capabilities of existing measurement platforms to support observations over broad areas of ocean where peak heating of the capsule was expected to occur. Then the team ascertained the performance of the optical measurement systems associated with these platforms. The performance of the optical systems was judged based upon past performance, likelihood of long-range acquisition from extreme distances, and determination of the expected spatial resolution of the resulting thermal imagery near the point of closest approach between the capsule and the imaging system.

Next, image degradation from atmospheric effects, shock-layer radiation, and the presence of the heat shield TPS ablation products was estimated using state-of-the-art tools. The NESC team’s draft findings, observations, and recommendations from this initial assessment were presented to the stakeholders and the NESC Review Board (NRB) for approval. The recommendation to proceed to the second phase was approved. Based upon a successful infrared observation on December 5, 2014, the quality of the data was reviewed by the team and presented to the Aerosciences Technical Discipline Team (TDT) for approval to proceed to the final analysis phase, whereby surface temperatures derived by the remote-based observations were compared to heat shield surface temperatures inferred from in-depth TCs. The final review was the NESC peer-review cycle. A preliminary presentation was made to Mr. Tim Wilson, Director NESC, summarizing the observation and results. Recommendations were made to enable more affordable and enhanced measurement capability to support Agency and National priorities in, but not limited to, hypersonic flight T&E.

6.0

Problem Description, Proposed Solutions, and Risk Assessment

FTOs are technical statements defining objectives to be accomplished during a test flight. The MOPs often associated with FTOs describe specific types of measures to be collected and a description of the predicted behavior, value, or environment that the measures will be used to confirm. The MPCV Program FTO OFT1.091 identified the requirement to determine the capsule heat shield and backshell aerothermodynamic environment during reentry. This type of FTO generally requires quantitative data to be collected to validate a mathematical prediction of subsystem performance and/or environment. One of the three MOPs identified with OFT1.091 specified an observation during reentry though external ground-based or airborne assets with thermal detection capabilities.

(20)

The FTO objective was to be met with onboard DFI, and the MOP for external observation was intended to complement and serve as a risk reduction in the event of anomalous DFI behavior (or failure). For example, anomalous TC behavior in the form of large voltage fluctuations yielding non-physical temperatures has been documented in over 29 Shuttle hypersonic reentries. Root cause was never identified but was likely due to interactions of the TCs with plasma in the shock layer. Furthermore, failure of DFI recording hardware and loss of data was experienced during an early uncrewed Apollo test flight (AS-201) and the SSP during STS-1, STS-4, and STS-35. As such, Mr. Gavin Mendeck, the EDL Phase Engineer for the MPCV Program (Vehicle Integration Office/Systems & Mission Integration), requested a risk-reduction assessment from the NESC to determine whether quantitative thermal imagery could be obtained from remote aerial assets to support the external observation MOP. For the purposes of the assessment, thermal was interpreted as infrared signatures at sufficient accuracy to compare against in-situ TCs and at a spatial resolution to discern potential localized heating in the vicinity of heat shield surface features like the compression pads. If so, then a viable path forward was to be

determined, risks identified, and an observation pursued. If not, then the MOP for external observation was to be eliminated. Time-resolved but spatially unresolved measurements of absolute spectral radiance from the MPCV capsule and its trailing wake during reentry were not considered.

6.1

Challenges with Heat Shield Thermocouples

Figure 6.1-1 shows the distribution of thermal measurement DFI on the heatshield: (19) four-junction TC plugs and (14) two-four-junction TC plugs are located on the heatshield. Also shown are the locations for the pressure instrumentation associated with Flush Air Data System (FADS) and radiometers. Because of the sparse TC spatial distribution on the heat shield as shown Figure 6.1-1, the nature of an image-derived global temperature map would make it possible to fill in these gaps for a brief time period during reentry. Also evident in the figure are the six compression pad locations near the periphery where the heat shield is attached to the service module. An example of a four-junction TC plug is shown in Figure 6.1-2. As viewed from the side of the plug, the TC junctions are not placed at the surface, but rather in depth in anticipation of heat shield recession and to protect them from the harsh conditions during reentry.

The desire to complement the TC DFI heat shield instrumentation with image-derived

temperature inferred from remote infrared observation is coupled to the complex processes of collecting quality measurements and then reconstructing surface temperature from the in-depth TC measurements. It was anticipated that interpretation of the EFT-1 flight TC data would be challenging if past non-physical surface temperature, as exhibited by TC measurements during SSP orbiter reentry, was experienced during EFT-1. The non-physical temperatures resulting from large voltage fluctuations in the TCs can make it impossible to provide accurate data from which to validate engineering models and difficult, if not impossible, to reliably infer boundary layer transition from a temperature time history trace. The MPCV Program viewed the EFT-1 thermal observation as a risk reduction in the event of such DFI TC anomaly, recording hardware failure, or to aid in reconstruction in the event of a vehicle mishap during reentry.

(21)

As discussed in a report issued 90 days after the EFT-1 recovery [ref. 21], the process to

reconstruct surface temperature from in-depth TC temperature measurement requires an inverse heating method. The method necessitates accurate knowledge of the in-depth thermal properties of the material in which the TC is embedded so that an inverse heat transfer method can be applied to extrapolate the temperature measured at the junction to the surface. Post-processing of the flight TC measurements using an inverse heat transfer numerical method is complex and can be time-consuming to implement. Uncertainties arise from assumptions in time-dependent material properties and depth of the ablative TPS char layer in the vicinity of the in-depth TC. Surface temperatures derived by the remote-based observations associated with this assessment were presented as a direct and independent method to infer surface temperature and hence verify the performance of the material response methodology.

Figure 6.1-1. Schematic of EFT-1 Heat Shield DFI Instrumentation Layout (Subsurface TC Locations Identified in Blue and Red)

While nothing will replace the value of in-situ instrumentation, the challenges of minimizing DFI impacts to vehicle weight and internal complexity, and inherent instrument bandwidth limitations often restrict the ability to make high spatial density in-situ measurements. Thus, remote

(22)

unique and critical flight data without interfering with nominal vehicle operations, weight, performance, and scheduling.

Figure 6.1-2. EFT-1 Heat Shield TC Plug (Side View Showing TC Junctions below the Surface with Outer Surface Shown on the Image Top)

6.2

Platform and Instrument Capability

At the heart of this assessment is the question of whether existing remote thermal sensing capabilities can address the MPCV Program’s requirement of an observation as a risk reduction while providing useful, engineering-quality data. To answer this question, an analysis was undertaken to determine: where the observation would most likely occur, what type of imaging platform would be required, and whether the optical system associated with that platform would provide useful spatial resolution. Approximately 18 months prior to the EFT-1 launch, reentry trajectory information was provided to the NESC team to determine where the desired thermal observation would occur. The trajectories were imported into a synthetic virtual modeling environment from which to visualize the reentry path (herein referred to as the ground track) as shown in Figure 6.2-1. The inset graphic shows the 2 ½-orbit flight path from launch to recovery point. The synthetic modeling tool used to generate this graphic is discussed in more detail in Section 6.3, Risk Characterization and Mitigation.

(23)

Figure 6.2-1. EFT-1 Proposed Reentry Flight Path (circa 2013) with Splashdown off the Coast of California

Ground-based systems have demonstrated superior spatial resolution performance and some level of mobility. The best spatial resolution obtained on a reentering spacecraft at hypersonic speeds was acquired with a mobile ground-based infrared imaging system during a reentry observation of the SSP orbiter Endeavor in 2011 [ref. 16], as shown in Figure 6.2-2. At a range of 32 nautical miles (nmi), the estimated spatial resolution on this thermal was approximately 4 inches per pixel. At this resolution, the individual carbon-carbon wing leading edge panels can be discerned.

(24)

Figure 6.2-2. Thermal Image of Endeavour During STS-134 Reentry Near the Point of Closest Approach, Mach 5.8, Slant Range ~32 nmi. (Estimated resolution ~4 inches per pixel.)

However, experience has shown that mobile ground-based imagers are susceptible to longer atmospheric path lengths, turbulence near the ground, and obscuring clouds. As indicated in Figure 6.2-1, peak heating during EFT-1 reentry was anticipated to occur over the Pacific Ocean with crew capsule recovery approximately 600 nmi off the California coast, which is absent of any remote land islands capable of providing imaging from the ground. Therefore, any mobile or fixed ground-based imaging assets (e.g., the Air Force Maui Optical and Supercomputing observatory) were excluded from consideration. Sea-based imaging systems inherently possess all the challenges of a ground system along with other inherent concerns. In addition to making an observation through an image-degrading marine layer with high aerosol content, pointing stability requirements at sea associated with narrow field-of-view (FOV) optics represents a significant hardware integration challenge in terms of gyro-stabilization and isolation from the ship motion and engine vibrations. Therefore, sea-based imaging platforms were not evaluated. Naturally, imaging strategies over remote bodies of water tend to favor the flexibility and range of airborne systems. Five aerial platforms were initially considered by the NESC team and are listed in Table 6.2-1.

(25)

Table 6.2-1. Initial Set of Aircraft Imaging Platforms Considered for the EFT-1 Thermal Observation

Aircraft

Transit

Range, nmi

Endurance, hr Max Altitude, ft

NASA DC-8 5,400 12 41,000 NASA WB-57 2,500 6.5 60,000 NASA SOFIA 747SP 6,600 9 45,000 NASA HU-25 2,000 7 40,000 L-3 HALO II GIII 3,500 7 51,000 Navy NP-3D (BH-300) 4,000 12 30,000

With the exception on the Navy NP-3D aircraft, all platforms initially considered operate at altitudes of greater than 40,000 ft. At these altitudes, risks from obscuring cloud coverage is essentially avoided and the undesirable optical absorption effects in the infrared spectrum from water vapor and scattering from aerosols is greatly diminished. Relatively speaking, aircraft at these altitudes are positioned closer to the intended target further mitigating detrimental

atmospheric effects. Three aircraft (highlighted in red in Table 6.2-1) were eliminated from contention for several reasons. The DC-8 and Stratospheric Observatory for Infrared Astronomy (SOFIA) 747 aircraft serve as workhorse measurement platforms for NASA’s Science Mission Directorate and they are used extensively for Earth/atmospheric science and astronomy,

respectively. Schedule conflict risk was extremely high with these platforms. In addition, sensors and instrument operator expertise must be provided when utilizing the DC-8. The SOFIA 747 is configured with an infrared sensor, but since it is essentially staring for

astronomical purposes, it is not possible to track a moving target at the high angular velocities required for an EFT-1 observation. The High-Altitude Observatory (HALO) II Gulfstream III platform supports observations associated with the Missile Defense Agency (MDA), but its sensor package could not be modified/optimized for the expected photon-rich infrared observation of the MPCV capsule heat shield.

Of the three remaining aircraft, the NASA HU-25, a converted Falcon business jet, was

considered for a longer period of time during the assessment. It was eliminated from contention when it was determined that an imaging/tracking system being designed and built for use on this aircraft would not be operational on the projected EFT-1 launch date in December 2014. The remaining two viable aircraft (i.e., BH-300 and the NASA WB-57) are multi-engine aircraft that routinely support over-water operations. Each hosts its own sensor package and provides instrument operational expertise. Following the optical analysis described in Section 6.3, these aircraft were shown to produce acceptable spatial resolution with their respective infrared imaging systems. Despite its larger susceptibility to weather constraints, the Navy NP-3D was selected as the primary imaging aircraft largely because of its demonstrated experience base tracking high-speed moving targets under the NESC HYTHIRM project, and its longer

endurance/loiter time. The Navy NP-3D aircraft shown in Figure 6.2-3 is stationed at the Naval Air Warfare Center, Point Mugu Naval Air Station, California.

(26)

Figure 6.2-3. U.S. Navy NP-3D Cast Glance Aircraft (Bloodhound 300 (BH-300))

The optical system on the BH-300, often referred to as Cast Glance, comprise a set of electro-optical platforms mounted within the aircraft pressurized section (Figure 6.2-4). A gyro-stabilized gimbaled mirror tracks the target and directs the light toward a fixed telescope rather than moving the camera and lens. Through a series of beam splitters and pick-off mirrors, light is diverted to several video, digital and high-speed visual, and infrared imaging sensors. The gimbaled mirror can be steered manually or assisted through the aid of a computer-aided pointing system. Aircraft flight data and target position information can be embedded into the video fields. A typical crew complement includes seven aircrew and four Cast Glance sensor operators. The aircraft operates nominally at an altitude of 25,000 ft but can climb higher as long as the internal cabin pressure can be maintained to a pressure equivalent to 10,000 ft (or below). The NP-3D is capable to reaching 40,000 ft, but it would require the supplemental use of oxygen to avoid hypoxia.

Figure 6.2-4. Internal Layout of the Navy NP-3D Orion (BH-300)

Spectral wavelengths of the Cast Glance systems include visible (0.4 μm to 0.7 μm), near-infrared (NIR) (0.7 μm to 1.1 μm), shortwave near-infrared (SWIR) (0.9 μm to 1.7 μm), midwave infrared (MWIR) (3.4 μm to 4.9 μm), and longwave infrared (LWIR) (7.5 μm to 13.0 μm).

(27)

The NASA WB-57, shown in Figure 6.2-5, is based at Ellington Field, Houston Texas and was maintained as a potential backup in the event mechanical or schedule issues precluded the use of the Navy NP-3D Orion aircraft. The platform from which this aircraft is derived was designed for high-altitude reconnaissance in the 1950s, and the NASA variant can reach an altitude in excess of 65,000 ft. The crew consists of the pilot and a sensor operator sitting inline in a front- and backseat configuration. As with Cast Glance, tracking is performed manually or with a computer-assisted auto tracking system. The WB-57 is capable of carrying a variety of electro-optical payloads in different locations on the airframe, including wing pods, a modified “bomb bay,” and a nose pod housing a gyro-stabilized ball turret referred to as the Day/Night Airborne Motion for Terrestrial Environments (DyNAMITE) ball turret imaging system (see Figure 6.2-6). Spectral wavelengths of the DyNAMITE system considered for EFT-1 imaging include high-definition visible (0.4 μm to 0.7 μm), and MWIR (3.4 μm to 4.9 μm) imagers.

Figure 6.2-5. NASA WB-57 with Nose-Mounted DyNAMITE Imaging Sensors

(28)

6.3

Risk Characterization and Mitigation

The SSP observation campaigns from 2009 to 2011 resulted in remarkable thermal imagery yielding global surface temperature maps from seven successful infrared observations. Relative to the SSP orbiter, the EFT-1 capsule is significantly smaller in size and, as a result, surface temperatures were expected to be up to a factor of 2 higher during reentry. For comparative purposes, the relative size and expected temperature difference between the SSP orbiter and an early MPCV capsule configuration is shown in Figure 6.3-1. Given these fundamental

differences, it was not clear at the beginning of the assessment if the target (MPCV capsule) could be acquired at extreme distances, if sufficient spatial resolution could be achieved at the point of closest approach, and/or if the higher surface temperatures and the ablative nature of the heat shield TPS would preclude useful surface temperatures derived from the infrared imagery.

Figure 6.3-1. Relative Size and Temperature Differences between SSP Orbiter and the MPCV Capsule

To answer these and other questions, the NESC team utilized a number of simulation tools developed and tailored for use by the SCIFLI team prior to the observation. These simulation tools allowed the team to set expectations with the technical stakeholders and ultimately provide the sensor operators and flight planners with synthetic imagery from which to formulate

deployment recommendations, determine pre-flight sensor configuration options, and locate optimal aircraft observation locations. The use of the modeling tools served as an essential element of risk mitigation. This section lists several risk topics identified by the team. A question is first stated pertaining to the risk topic. A risk statement is then presented (with risk context if appropriate). A description of the tools and how they were used to characterize and/or mitigate the risk is then provided. The risk topics are not necessarily listed in order of priority but more in terms of when the specific risk might be encountered during an observation campaign (e.g., in a chronological fashion).

(29)

6.3.1 Location of Peak Heating

Where along the EFT-1 reentry flight path does peak heating on the heat shield occur, and can an aircraft transit to and from that general location with sufficient loiter time?

Risk: Given the number of variables in determining when and where peak heating will occur, there is a possibility that the location will not be identified until the day of reentry.

Risk Context: Variables include, but are not limited to, final EFT-1 entry trajectory, vehicle weight, aerodynamic performance, when the onset of boundary layer transition will occur, and atmospheric uncertainties.

Assessment and Mitigations: In contrast to the SSP, where a 90-min (or 48-hour) delay in returning from low Earth orbit would significantly shift the ground track, the EFT-1 ascent and subsequent reentry ground track was not susceptible to these shifts. That is, for any given launch time, the location of the flight path relative to the Earth remains unchanged. Therefore, the process of determining the general location of the peak heating event relative to any fixed point on Earth was less complex. The position along the flight path where the EFT-1 capsule

experiences maximum heat shield temperature (i.e., peak heating) was specified from a fixed point in time, either from capsule separation from the Delta IV upper stage or from Entry

Interface (EI), which was designated as an altitude of 400,000 ft. Dispersions in the peak heating location resulting from uncertainties in the performance of the Delta IV Heavy launch vehicle upper stage, the capsule aerodynamics, and the upper atmosphere were later characterized by a series of Monte Carlo simulations. The uncertainty ellipse of the peak heating location provided to the NESC team was found to be relatively small (~50 nmi) compared to the required transit distances.

The Virtual Diagnostic Interface (ViDI)[refs. 22-25] tool was used to provide insights regarding the location of peak heating as identified by the EFT-1 Aerosciences team. In this software package, 6-degree of freedom trajectory information and the timing of critical events are

imported and tied in with commercial off-the-shelf graphical software to visualize aspects of the entire trajectory on a virtual three-dimensional (3-D) Earth. Figure 6.2-1 represents an example of the output and shows the EFT-1 flight path relative to the west coast of California. Mach number or other desired information can be readily incorporated in the graphics. The initial peak heating location was approximately 600 nmi from the west coast of California, thus within reach of all the aircraft initially considered in Table 6.2-1. With the ability to stay aloft for

approximately 11 hours, the Navy NP-3D would only require 23 hours of one-way transit time to reach the general area for the desired observation leaving 45 hours of loiter time.

6.3.2 Observation Location and Estimated Spatial Resolution

Where is the desired observation location from which peak heating is to be observed during EFT-1 reentry, and will spatially resolved thermal imagery be possible?

Risk: Given the number of variables in determining the final location of the aircraft, there is a possibility that the optimal test support point (TSP) will not be identified until the day of reentry.

(30)

Risk Context: Variables include, but are not limited to, local weather, EFT-1 launch timelines, aircraft performance parameters, Sun position, EFT-1 entry trajectory, and hazard zone

boundaries. The geometry between the observing aircraft and the target vehicle determines elevation angle, system slewing rates, spatial resolution, aircraft maneuvers to maintain the capsule in the field of regard (FoR), and the total viewing time.

Assessment and Mitigations: Additional information in the form of surface computer-aided design (CAD) definition is imported into the ViDI tool to ascertain and then graphically display the spatial resolution performance of the imaging system. Lockheed Martin provided the EFT-1 surface CAD geometry for this phase of the assessment. The ViDI program pulls optical system specifications from an asset database (e.g., a particular telescope mount on an aircraft or a land-based system) and determines the view/orientation of the target land-based on the asset position and the location of the target during reentry. Information in a preliminary EFT-1 trajectory file, provided in 1-Hz increments, was used with the surface CAD to create dynamic synthetic imagery in the interactive 3-D virtual environment. A scaled representation of the flight test vehicle was located and orientated at each time step specified in the trajectory file. Entering latitude, longitude, and altitude defined the location for a virtual camera on the Navy NP-3D aircraft. Both the virtual camera FOV and the pixel resolution were matched to the performance of optical system carried on the aircraft, thus rendering a pixel-to-pixel accurate simulation of the expected imagery. A simulation of this nature only captures the expected spatial characteristics (e.g., viewing perspective, pixels on target) but is not radiometrically accurate.

An example of the ViDI output, Figure 6.3.2-1, depicts the spatial resolution performance of the Cast Glance NIR camera as configured for an observation near the expected point of peak heating. Based upon the sensor and telescope specifications and the capsule at a nominal slant range (i.e., distance from capsule to aircraft) of 37 nmi, each pixel associated with the NIR sensor represents approximately 10 inches. Some image degradation from the atmosphere and the optical system, and blurring due to jitter and motion of the aircraft, was expected to decrease the resolution of the unprocessed imagery to 1215 inches per pixel. At this resolution, thermal features (e.g., the boundary layer transition if present during the observation period) could be readily identified. Localized temperature gradients expected within the compression pads (Figure 6.1-2) would not be spatially resolved, but the averaged elevated temperature in the general vicinity could be detected over several pixels. As such, the estimated spatial resolution and the heat shield viewing perspective obtained with the Cast Glance imaging system

positioned for an observation near the peak heating event was acceptable to the FTMO and the MPCV engineering community.

(31)

Figure 6.3.2-1. Synthetic Image of MPCV Capsule near the Point of Peak Heating as Viewed from the Navy NP-3D Aircraft

The synthetic imagery-based representation of spatial resolution as shown in Figure 6.3.2-1 is one point in time. The ViDI tool can output the estimated spatial resolution on the target as a function of time as shown in Figure 6.3.2-2 (aircraft position is located outside of the hazard zone and optimized for frontal view of capsule heat shield at peak heating). It is important to recognize the estimated 10-inch-per-pixel resolution will be experienced over a relatively brief time period (i.e., 1015 sec) relative to the possible horizon-to-horizon observation time (i.e., 46 min).

For safety considerations and tracking constraints, the aircraft cannot be located directly under the EFT-1 flight path. Typically, the aircraft is positioned offset from the ground track some predetermined distance. The NAVY NP-3D standoff distance from the EFT-1 ground track was based upon elevation constraints looking through the aircraft window and keep-out zones imposed by hazard analysis of a potential capsule break up. Lockheed Martin and NASA analysts supporting the MPCV FTMO provided a Flight Dynamics Range Safety Data Package to the NESC team that detailed and enveloped all worst-case scenario debris during a failed crew capsule reentry. This keep-out zone dictated the standoff distance (and thus slant range) used in the spatial resolution analysis presented in Figure 6.3.2-1. To account for a hypersonic capsule breakup and dispersions in the atmospheric entry point, the aircraft standoff distance from the nominal EFT-1 ground track was required to be at least 27 nmi to ensure crew safety. In the unlikely event of an anomaly during reentry, communication to alert the aircraft via high-frequency (HF) radio and/or Iridium phone was planned at regular intervals. The relationship between the EFT-1 ground track, the keep-out zone boundary, and the Navy NP-3D flight is

(32)

shown in Figure 6.3.2-3. Blue points indicate timed locations of the Navy NP-3D as the capsule approached the point of peak heating.

NASA Langley Research Center

Scientifically Calibrated In FLight Imagery

0 10 20 30 40 50 60 70 80 90 3040 3065 3090 3115 3140 3165 3190 3215 3240 3265 3290 In ch e s p e r P ix e l

Time from CM sep, seconds

Cast Glance NIR Inches per Pixel

Peak heating

Direct Side View

4.5 minutes to splashdown

9 seconds

NIR Inches Per Pixel, aircraft placement optimized for peak heating observation

BH-300 Forward Station Near IR Digital Imager FOV 0.15' x 0.15‘

spectral band 0.7um to 1.1um

resolution 1380/1024 X 1024 CMOS array radiometric calibration

Figure 6.3.2-2. Estimated Spatial Resolution of the Cast Glance NIR as a Function of Time

Figure 6.3.2-3. EFT-1 Ground Track and Hazard Keep-out Zone

The ViDI tool permits the user to determine the Sun’s position as a function of time. Such advance knowledge is essential to avoid difficulties in long-range acquisition, or permanent

(33)

damage to the infrared sensors by inadvertent pointing into the Sun. The requirement to recover the capsule in daylight conditions dictated an early morning launch from Cape Canaveral Air Force Station, FL. The subsequent reentry, approximately 4.5 hours later in the Pacific, placed the Sun in a favorable position for imaging (i.e., the angular position between the Sun and the capsule as viewed from the aircraft was 20° or greater at all times). The Cast Glance personnel performed an independent analysis of optical tracking line-of-sight plotted against the Sun’s azimuth and elevation throughout the planned observation interface. Should a conflict arise, positional shifts are considered to mitigate Sun influence. While repositioning is not always possible, it is important for the Cast Glance sensor operators to be cognizant of the Sun angle to determine proper sensor settings and to anticipate any visual difficulties in maintaining track. For MPCV’s crew capsule proposed entry time, the Sun was expected to be in an advantageous location for imaging and acquisition. The anticipated rates for the gimbaled mirror to maintain the capsule in the FoR were evaluated by the Navy personnel and were found to be acceptable (see Appendices F and G).

6.3.3 Asset Reliability and Schedule Conflict

Could mechanical failure or schedule conflict prevent the primary aircraft from supporting the observation?

Risk: Given that the Navy NP-3D supports DoD and other NASA missions, there is a possibility the aircraft will be unavailable to support the EFT-1 observation.

Risk Context: Navy NP-3D support to national priorities (e.g., support to MDA and DoD missions) take priority over NASA missions.

Assessment and Mitigations: Over a period of approximately 10 years, Cast Glance has

supported over 25 observations of Expendable Launch Vehicle for the DoD (numerous classified DoD missions were not considered). During this timeframe, only three aircraft mechanical system failures have prevented an observation. All three incidents occurred when the squadron was forward deployed with limited access to maintenance. Aircraft mission readiness to support 10 NASA imaging missions since 2009 has been 100%. From this data set, Cast Glance mission readiness is approximately 93%. Given the general location of the EFT-1 observation off the coast of California, it was determined that the Navy NP-3D could support the EFT-1 observation from its home base at Naval Air Warfare Center Weapons Division located at Point Mugu Naval Air Station, California. Staging from its home base would provide readily available access to maintenance and was pivotal during the mission.

As the assessment evolved, the MPCV Program determined that an FTO associated with capsule visual photo-documentation during late-stage descent (i.e., parachute deployment sequence) required the use of a second Navy NP-3D. Normally, the second Navy NP-3D would serve as a backup to the primary Navy NP-3D for imaging. Tasking the second Navy NP-3D to descent imaging raised the question of aircraft priority. The MPCV Program determined that should a mechanical failure or schedule conflict develop with this second Navy NP-3D, the NESC-sponsored aircraft for peak heating would be re-tasked to support descent imaging. The NESC

(34)

Aerosciences TDT lead was briefed on the MPCV Program priority and accepted the possibility of no thermal imagery should a schedule or mechanical risk mature.

Securing the services of the NASA WB-57 aircraft as a backup to the Navy NP-3D mitigated schedule risk. A few months from the scheduled EFT-1 launch, permission was granted by the NESC to allocate contingency resources toward securing WB-57 flight planning services. These planning services, obtained through The Aerospace Corporation, provided the pilot and sensor operator with sufficient background on the observation requirements in the event the aircraft had to used. The flight path and optical performance of the NASA WB-57 was determined through the use of a custom tool developed by The Aerospace Corporation called Chase Plane Simulation (ChaPS). ChaPS provides similar functionality as the ViDI toolset, but was optimized for

designing detailed flight paths for aircraft with gimbaled turret sensors such as the WB-57. The target vehicle trajectory and aircraft sensor information are inputs, as are candidate aircraft flight paths. Similar to ViDI, the tool outputs detailed 3-D representations of the aircraft optical platform, with dynamically modeled gimbals. The simulated relationships between the aircraft, camera-pointing hardware, and the target vehicle are assessed with ChaPS. Figure 6.3.3-1 shows an example of the flight planning associated with the WB-57 aircraft. Yellow points in the figure indicate timed locations of the WB-57 as the capsule approached peak heating.

(35)

6.3.4 Long-Range Acquisition

At the designated observation location, will the sensor instruments have sufficient sensitivity to acquire and track the capsule?

Risk: Given the expected low surface temperature of the MPCV capsule prior to EI, there is a possibility that the long-range wide field of view (WFOV) sensors will have insufficient sensitivity to acquire the target as it appears over the horizon.

Risk Context: The MPCV capsule will not broadcast a signal of its position. Positional data that are telemetered will experience time lags.

Assessment and Mitigations: Previous SCIFLI observations were successful at long-range acquisition because the vehicle surface temperatures were in excess of 1000 °F, providing high signal-to-noise ratio as the vehicle emerged over the hard Earth horizon. If the infrared signature of the capsule was too weak and it was not detected long-range at low angular velocities, then experience has shown it would be more difficult to acquire at higher angular velocities when the target approaches the aircraft.

The NESC team utilized a set of planning tools to establish processes and recommendations for reliably acquiring and tracking the EFT-1 capsule during reentry. In contrast to ViDI, these tool sets allowed the user to quantitatively characterize the optical signature presented by the capsule to infrared sensors, to assess the attenuating and image degrading effects of the atmosphere, and to determine the anticipated sensor response in the infrared. This section discusses how the optimal infrared waveband was determined for long-range acquisition and spatially resolved viewing at the point of peak heating. During the early stages of the assessment, the implications of the potentially attenuating effects of ablation and shock-layer radiation during the peak heating observation were recognized, but not considered due to the problem complexity. These effects will be discussed in Sections 6.3.67.

The basic principle behind infrared thermography is the measurement of surface emissions in the infrared radiation band by virtue of an objects temperature. The infrared radiation spectrum is classically divided into several bands as identified in Figure 6.3.4-1.

NIR 0.81.5 μm SWIR 1.53.0 μm MWIR 3.05.0 μm LWIR 515 μm Far Infrared 15300 μm

(36)

Figure 6.3.4-1. Blackbody Radiance Characteristics

The capsule optical signature (i.e., irradiance) was based on the predicted surface temperature provided by computational fluid dynamics (CFD). Predicted temperatures on the EFT-1 heat shield during several phases of reentry are shown in Figure 6.3.4-2. Time zero in this figure corresponds to when the capsule is separated from the Delta IV upper stage, with the capsule recovery in the Pacific occurring approximately 1 hour later. From the vantage point of the imaging aircraft, the capsule was expected to appear over the Earth’s horizon (at a distance of 1,330 nmi) approximately 5 minutes before the capsule reached its maximum surface

temperature. As the EFT-1 capsule would not be broadcasting its positional information real time, it was imperative to develop an acquisition strategy to permit the sensor operator to quickly locate the capsule and begin manual tracking. To initially locate the capsule, the optical system on the aircraft would be pointing at a predetermined point in the sky based upon a projected flight path. At the horizon break, the capsule heat shield was expected to be approximately 40 °F (277 K) because the initial line-of-sight view from the aircraft would occur when the capsule was exoatmospheric and before the frictional heating from the atmosphere. At this temperature, a perfect blackbody radiation source would have its irradiance peak in the LWIR waveband as shown, Figure 6.3.4-1, but its signal strength in this waveband would be relatively small and likely problematic from a detector sensitivity perspective. When the capsule was one minute from passing the observing aircraft, the heat shield temperature was expected to increase to approximately 1300 °F (977 K). At peak heating, the surface temperature was expected to increase by from its baseline temperature by two orders of magnitude, to approximately 4,000 °F (2,477 K). Extrapolation of the trends in Figure 6.3.4-1 to this temperature level suggested the NIR waveband would likely be targeted for the desired spatially resolved thermal measurement. Given the rapidly changing surface temperature during this time period, it was apparent the sensor operator would need to be prepared to monitor detector saturation levels and adjust the sensor exposure time should these levels be approached.

(37)

Figure 6.3.4-2. Predicted Surface Temperatures on the EFT-1 Capsule during Several Phases of Reentry

During an SSP observation using the same Navy NP-3D and NIR sensor, the high temperature capsule windward surface (~1,500 °F/1,089 K) presented a strong photon-rich emission in the NIR waveband as it emerged over the horizon. In these observation campaigns, a WFOV NIR imager would manually acquire, track, and provide pointing instructions to the narrow FOV NIR imager utilized to provide the spatially resolved thermal data. It was initially assumed this long-range acquisition strategy would be viable during the EFT-1 flight test. When it was determined the capsule heat shield would have a surface temperature an order of magnitude lower than the SSP orbiter at horizon break (~4050 °F), it was concluded the capsule would be significantly more difficult to distinguish from the sky background using the Cast Glance NIR WFOV sensor. It was assumed sufficient signal strength would appear in the more photon-rich MWIR band for acquisition and tracking purposes when the capsule was at extreme distance, spatially unresolved (i.e., a point source), and at low temperature. Through high-fidelity radiance modeling, this assumption was proved incorrect.

The high-fidelity radiance modeling tools used by Johns Hopkins University Applied Physics Laboratory (JHU-APL) are derived from an off-the-shelf code [refs. 26-27] traditionally used by the DoD to support an advanced scene generation capability. Under a previous NESC

assessment [ref. 1], the code has been tailored for use by NASA and it was used for this

assessment to produce simulated capsule heat shield infrared signatures. This radiance model is fundamentally built around capsule laminar and turbulent CFD surface-temperature predictions over a range of Mach numbers. The radiance modeling simulated the infrared sensor response to

(38)

the estimated target vehicle irradiance based on surface temperature, emissivity, and reflectance. Because the Sun’s radiation, aerosols, and molecular scattering are particularly important

background sources, the atmospheric absorption and radiation emission are additional parameters that must be considered when inferring the target surface temperature from infrared emission. Characteristics of the infrared sensor and associated optical system were considered. The radiometric analysis by JHU-APL determined the ability of a particular sensor to obtain measurements with acceptable signal-to-noise ratios under given camera settings. In the

waveband of interest, atmospheric effects (e.g., radiance and transmittance) were estimated with the radiative transfer code MODTRAN®_{[ref. 28], which is designed to model the propagation of} electromagnetic radiation through the atmosphere.

Surface optical properties are critical for accurately predicting the thermal irradiance from the capsule in the desired waveband of interest (i.e., spectrally integrated surface emissivity across several wavebands is insufficient). Emissivity is a measure of how closely the radiation emitted from a heated body corresponds to that of a perfect blackbody. Laboratory material testing was required to determine in-band surface emissivity of the EFT-1 capsule heat shield. Surface roughness and reflectance characteristics can strongly influence emissivity, so EFT-1 specific TPS surface material samples were provided to the Surface Optics laboratory to conduct laser-based measurements to characterize their respective surface optical characteristics both spectrally and angularly (see Appendix A). The Avcoat TPS samples represented the virgin and

charred/ablated state after exposure to a high-temperature environment produced in an arcjet. Images of the TPS samples used in these laboratory measurements as shown in Figure 6.3.4-3. During this phase of the assessment, it was learned that to control the heat shield thermal

environment while in orbit, the Avcoat surface would be coated with a white epoxy enamel paint and covered by a thin aluminized Kapton® film. While these materials would ablate after EI, it would be present during the long-range acquisition from the aircraft. This had implications in terms of the long-range acquisition strategy.

(39)

The laboratory measurements revealed the aluminized surface would significantly attenuate the capsule irradiance in the MWIR, thus presenting significant risk in an acquisition strategy using the MWIR waveband as had been assumed. As shown in Figure 6.3.4-4, the metallic tape measurements over a range of viewing angles indicate a low value of emissivity for wavelengths greater than 2 μm (i.e., the MWIR/3.0-5.0 μm and LWIR/ 5-15 μm wavebands).

Figure 6.3.4-4. Measured Emissivity of Aluminized Kapton® Tape

The emissivity measurements on the charred Avcoat yielded higher values, as shown in Figure 6.3.4-5, confirming the NIR waveband as suitable for the spatially resolved thermal observation after long-range acquisition and tracking had been achieved.

Figure 6.3.4-5. Measured Emissivity of Charred/Ablated Avcoat

Based upon the laboratory measurements, it was decided to develop a long-range acquisition strategy centered around the Cast Glance SWIR WFOV sensor where a higher signal-to-noise ratio provided a better opportunity to distinguish the capsule from the sky background.

(40)

Figure 6.3.4-6 provides an example of the radiance model output. At a range of approximately 500 nmi, the capsule is spatially unresolved. The effects of blurring from the atmosphere and aircraft motion estimated and yielded a signature that is a factor of approximately 1.5 higher than the background sky irradiance. The corresponding signature for the MWIR waveband (not shown) was less than 50% of the background sky radiance that rendered acquisition of the capsule in this waveband improbable. For estimating the atmospheric attenuation and

atmospheric radiance background, the 1976 U.S. Standard Atmospheric model was used with optimistic maritime settings (e.g., maritime haze and no clouds).

Figure 6.3.4-6. Predicted Irradiance in SWIR Waveband at Time of Long-Range Acquisition. Distance to Capsule = 493 nmi. Elevation Angle = 3 deg. Signal-to-Sky Background ~1.5.

Additional analysis showed that during the long-range acquisition phase when the aluminized tape was in place and highly reflective, the irradiance from the capsule would be dominated, particularly in the SWIR waveband, by solar reflectance and not thermal emission. This solar irradiance, which is the result of a favora

Remote Imaging of Exploration Flight Test-1 (EFT-1) Entry Heating Risk Reduction

NESC-RP-12-00795

 CONFERENCE PUBLICATION.

 TECHNICAL TRANSLATION.

NESC-RP-12-00795

Acknowledgments

Remote Imaging of Exploration Flight Test-1 (EFT-1)

Table of Contents

Technical Assessment Report ... 7

7.0 Data Acquisition and Data Analysis ... 53

8.0 Findings, Observations, and NESC Recommendations... 87

Technical Assessment Report

Signature Page

Team List

Name Discipline Organization

Administrative Support

Acknowledgements

Executive Summary

Assessment Plan

Problem Description, Proposed Solutions, and Risk Assessment

Challenges with Heat Shield Thermocouples

Figure 6.1-1. Schematic of EFT-1 Heat Shield DFI Instrumentation Layout (Subsurface TC Locations Identified in Blue and Red)

Platform and Instrument Capability

Figure 6.2-1. EFT-1 Proposed Reentry Flight Path (circa 2013) with Splashdown off the Coast of California

Aircraft

Figure 6.2-3. U.S. Navy NP-3D Cast Glance Aircraft (Bloodhound 300 (BH-300))

Figure 6.2-5. NASA WB-57 with Nose-Mounted DyNAMITE Imaging Sensors

Risk Characterization and Mitigation

Figure 6.3-1. Relative Size and Temperature Differences between SSP Orbiter and the MPCV Capsule

6.3.2 Observation Location and Estimated Spatial Resolution

Figure 6.3.2-1. Synthetic Image of MPCV Capsule near the Point of Peak Heating as Viewed from the Navy NP-3D Aircraft

Scientifically Calibrated In FLight Imagery

Figure 6.3.2-2. Estimated Spatial Resolution of the Cast Glance NIR as a Function of Time

Could mechanical failure or schedule conflict prevent the primary aircraft from supporting the observation?

6.3.4 Long-Range Acquisition

Figure 6.3.4-1. Blackbody Radiance Characteristics

Figure 6.3.4-4. Measured Emissivity of Aluminized Kapton® Tape

Figure 6.3.4-6. Predicted Irradiance in SWIR Waveband at Time of Long-Range Acquisition. Distance to Capsule = 493 nmi. Elevation Angle = 3 deg. Signal-to-Sky Background ~1.5.